As far as garbage that has been separated and crushed in a garbage separator is concerned, a conventional garbage dryer is configured to contain the garbage in a drying chamber and then agitate the garbage for drying, or configured to pass the garbage through the drying chamber for drying.
However, the garbage has a high-moisture content, so that in a case where the garbage is used as waste-derived fuel, the garbage needs to be dried sufficiently.
In order for the garbage to be subjected to drying for a long time, a large drying chamber is required, posing a problem in terms of installation space and increasing fuel consumption. This further poses an environmental problem that harmful substances contained in a fuel gas are released to atmosphere to cause pollution.
As for wastes other than the garbage, such as sludge in a wastewater treatment plant, poultry manure, and food wastes such as okara, there may be a case where drying is performed not by using the dryer but carried out in the sun or wind; however, the drying in the sun or wind is extremely inefficient.
Patent Document 1 is a garbage drier for drying the garbage that has been separated and crushed in a garbage separator.
A configuration of the garbage drier is illustrated in FIG. 7. A drying chamber 2 has a thin rectangular body, in which laterally extending tubular bodies 6 are arranged in multiple (eight, in the drawing) tiers. The tubular bodies 6 communicate with one another, in such a manner that end portions on one side and on the other side of vertically adjacent tubular bodies are connected alternately by means of connecting portions 6A, to form a single body as a whole.
The uppermost tubular body 6 is provided with a feed port 7 communicating with outside the drying chamber 2, and the lowermost tubular body 6 is provided with a discharge port 8 communicating with outside the drying chamber 2.
Although not illustrated, a pressure cylinder for pushing garbage that has been thrown from a garbage throw-in port into the tubular body 6 is provided above the feed port 7. Further, a belt conveyer for conveying the garbage is provided below the discharge port 8.
Screw conveyers 12 are incorporated in the respective tiers of the tubular bodies 6 and disposed such that forward paths and backward paths are vertically alternate. Rotation of a motor 13 is transmitted by an interlocking mechanism including a chain 14 and a sprocket 15 to cause the screw conveyers 12 to rotate in the same fashion.
Surrounding areas of the tubular bodies 6 in the drying chamber 2 are filled with granules 16 such as heat-resistant glass or ceramics.
Steam outlet ports 17 through which steam generated in the tubular bodies 6 are provided in the respective connecting portions 6A connecting the tubular bodies 6. One ends of steam delivery tubes are connected to the steam outlet ports 17, respectively, and the other ends thereof are merged together to be connected to a steam introduction tube provided at an upper portion of a primary combustion chamber.
In the configuration as described above, the garbage is pushed into the tubular bodies 6 from the feed port 7 and conveyed while being squeezed by the screw conveyers 12, with the result that moisture contained in the garbage is separated therefrom in the tubular bodies 6.
The moisture separated from the garbage is turned into steam by hot air to which the tubular bodies 6 are subjected, and the steam is fed, by a supply means, from the tubular bodies 6 to the primary combustion chamber, where the fed steam is gasified.
The garbage drier disclosed in Patent Document 1 has the configuration in which the tubular bodies through which the garbage is conveyed are arranged in multiple tiers and communicate with one another, in such a manner that end portions on one side and on the other side of vertically adjacent tubular bodies are connected alternately to form a single body as a whole. Thus, the garbage is conveyed over a long distance and, accordingly, drying time becomes long. Therefore, even in a small drying chamber, the garbage can be sufficiently subjected to drying, which eliminates the need for a large installation space.
Further, the tubular bodies are heated by indirect heat, and surrounding areas of the tubular bodies are filled with the granules, preventing thermal deformation to increase durability.
However, the moisture content of the garbage covers a wide range from several tens to about 90 percent, and the same applies to the sludge in a wastewater treatment plant, poultry manure, and food wastes such as okara. In a case of wastes having a high-moisture content, a large amount of steam is generated in the tubular bodies 6 to produce so-called “roasting condition”, which extremely degrades combustion efficiency. That is, the generation of the steam in the tubular bodies 6 decreases a temperature in the tubular bodies 6, preventing the waste to be combusted from being completely carbonized.
The garbage drier disclosed in Patent Document 1 has a discharge means for discharging the steam generated in the tubular bodies 6. That is, the above-mentioned steam outlet ports 17 are provided, as the steam discharge means, in the respective connecting portions 6A connecting the tubular bodies 6. However, such discharge of steam from the connecting portions 6A is insufficient.
Thus, the generation of steam from the waste to be combusted in the tubular bodies 6 occurs over a long distance along the screw conveyers 12, preventing the generated steam from being discharged completely from the connecting portions 6A connecting to the ends of the tubular bodies 6. Application of a suction pressure or an air supply pressure for the discharge of steam causes wind flow to adversely affect a temperature rise of the tubular bodies 6.
Since the tubular bodies 6 are arranged in multiple tiers in the vertical direction and communicate with one another, in such a manner that end portions on one side and on the other side of vertically adjacent tubular bodies are connected alternately, to form a single body as a whole, the garbage is conveyed over a long distance, dried for a long time, and thus can be sufficiently subjected to drying even in a small drying chamber, which however, in turn increases fuel cost for burner combustion.
It can be considered that a suction tube for the discharge of steam is provided inside the tubular bodies 6; however, for doing so, it is necessary to increase a diameter of each of the tubular bodies 6, which in turn increases a size of the entire device.
In order to overcome such an inconvenience, Patent Document 2 tries to discharge steam generated from the waste to be dried in the tubular bodies.
A configuration of a drying/carbonizing device disclosed in Patent Document 2 is illustrated in FIG. 8. In a drying chamber 2, tubular bodies 6 each having a screw conveyor 12 therein are arranged in multiple tiers in a vertical direction so as to extend in a lateral direction. The tubular bodies 6 communicate with one another, in such a manner that end portions on one side and on the other side of vertically adjacent tubular bodies are connected alternately, to form a single body as a whole. The screw conveyers 12 are disposed such that forward paths and backward paths are vertically alternate. The tubular body 6 located at one end is provided with a feed port communicating with outside the drying chamber 2, and a tubular body 6 located at the other end is provided with a discharge port communicating with outside the drying chamber 2. In this drying/carbonizing device, exhaust branch tubes 9 are attached to an upper half of the tubular bodies 6 of the screw conveyor 12 at appropriate intervals in a length direction, and the exhaust branch tubes 9 are connected to a meandering exhaust tube 10 provided side by side with the tubular bodies 6 in its length direction.
As illustrated in FIG. 9, the drying chamber 2 is connected to a deodorizing chamber 1 by a two-chamber connecting duct 27 and heats combustion gas in the drying chamber 2 with a burner to decompose dioxin (800° C.). Both the drying chamber 2 and deodorizing chamber 1 are subjected to a negative pressure (blower suction), and reference numeral 3 denotes a suction blower therefor.